Television systems that receive digital video data streams that have been encoded and compressed require a decoder, such as an integrated receiver/decoder, to decode and decompress the incoming digital video data streams. To ensure proper operation of the decoder, it is necessary to perform tests to determine if the video decoders are properly decoding and decompressing the digital video data streams.
An organization called Moving Pictures Experts Group (MPEG) created standards to establish a standard coding and decoding strategy to try to minimize problems with inter-operability of equipment. Test bit streams are provided by the MPEG committee. The bit streams contain various types of content and are generated by feeding the video through the software MPEG encoder. The test bit streams provide adequate materials for testing the development of the MPEG algorithm. However, they fail to exercise all possible values of the MPEG parameters.
For many years, other suppliers have provided standard test bit streams for MPEG-compliance video testing. One current test is based on preserving an error through its testing cycle. An error is usually evidenced by the erroneous final image of the test sequence. There are several drawbacks associated with the current testing method.
One such drawback is that the results of the testing conditions are determined by human perception of the video images. When the error conditions are subtle, the testing operators are not always able to discern their existence.
Another drawback is that there are certain errors that are not suitable for testing using the current test bit stream method. Examples include integrated receiver/decoder timing error and frame skipping/repeating error. These problems go undetected because the current method does not include adequate timing information.
Yet another drawback is the conflict between the typical group of picture (GOP) structure used for testing and the practical GOP structure used for broadcasting. MPEG allows for one long group of picture (GOP) structure. However, this is not the typical structure for practical GOP use. Typically integrated receiver/decoders are designed to handle a limited GOP duration, which is usually one-half to one-second periods due to the requirement of starting video from a random position. Due to the emphasis on the human visual pass/fail conditions and real-time testing by the current “predictive” testing method, the error evidence has to be preserved until the video stops. Therefore, the testing video sequence can only be constructed in one long GOP.